The present invention relates generally to the data processing field, and more particularly, relates to an AC transfer switch utilizing semiconductor devices to switch between two or more AC lines.
Applications requiring an AC transfer switch are increasing. Information technology customers are required to run 24 hours a day, 7 days a week for 365 days a year. In order to achieve this kind of up time, many information technology customers are requiring their equipment to be plugged into two separate AC main grids. When a first AC line goes down, the information technology equipment will run off a second AC line. The two separate power grids are distributed throughout the customer""s facility.
Information technology equipment must be able to reliably, quickly and safely switch between a bad AC line to a good AC line without affecting equipment operation.
An AC transfer switch (ATS) is used to switch between the different AC lines. Conventional ATS designs typically use electromechanical relay devices to switch between two or more AC lines. Electromechanical relay devices are much slower and much less reliable than semiconductor devices. Previous architectures using semiconductor devices have not been able to meet safety agency approvals.
A need exists for an AC transfer switch (ATS) capable of reliably, quickly and safely switching between AC lines. It is desirable to provide an AC transfer switch (ATS) utilizing semiconductor components capable of reliably, quickly and safely switching between two or more AC lines.
A principal object of the present invention is to provide an AC transfer switch (ATS) utilizing semiconductor components. Other important objects of the present invention are to provide such an AC transfer switch (ATS) utilizing semiconductor components substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.
In brief, an AC transfer switch (ATS) for switching a system load between at least two AC lines is provided. A first bridge rectifier is connected to a first AC line for providing a first full wave rectified AC waveform. A first pair of oppositely poled silicon controlled rectifiers (SCRs) is coupled to the first bridge rectifier and to the system load. A second bridge rectifier is connected to a second AC line for providing a second full wave rectified AC waveform. A second pair of oppositely poled silicon controlled rectifiers (SCRs) coupled to the second bridge rectifier and to the system load. Control logic is coupled to a gate input of the first pair of oppositely poled silicon controlled rectifiers (SCRs) and a gate input of the second pair of oppositely poled silicon controlled rectifiers (SCRs) for applying one of the first full wave rectified AC waveform or the second full wave rectified AC waveform to the system load.
In accordance with features of the invention, the control logic includes a first AC line sense circuit for sensing the first AC line input and a second AC line sense circuit for sensing the second AC line input. A first optical isolator is responsive to an output signal provided by the first AC line sense circuit sensing the first AC line input within a predefined AC line tolerance for activating the gate input of the first pair of oppositely poled silicon controlled rectifiers (SCRs) and applying the first full wave rectified AC waveform to the system load. A second optical isolator is responsive to an output signal provided by the first AC line sense circuit sensing the first AC line input outside the predefined AC line tolerance and an output signal provided by the second AC line sense circuit sensing the second AC line input within the predefined AC line tolerance for activating the gate input of the second pair of oppositely poled silicon controlled rectifiers (SCRs) and applying the second full wave rectified AC waveform to the system load.